Relic of Yu'lon vs. Essence of Terror(Normal) both 2/2 upgraded

I'm replacing 1 of my trinkets with Heroic Light of the Cosmos. The thing is, im not sure which one to replace. I'm currently spec'd Arcane. The trinkets I have is Relic of Yu'lon and Essence of Terror (normal). They are both upgraded fully (2/2).

Which trinket is superior? Which one should I replace.

EDIT: I'm going for Mastery build (NOT haste)

Also, if I decide to change spec in the future for whatever reason, which trinket combo is best for Frost and/or Fire?

There's a very detailed list of trinkets in the arcane guide if that helps you at all.

I can tell you that for frost you want to use Frost Bomb with Essence of Terror and Relic of Yu'lon for low movement fights or fights with adds. For heavy movement fights you would swap the Relic of Yu'lon for Light of the Cosmos and use Nether Tempest.

Im sorry I forgot to mention it in the original post, but; I'm going for Mastery build (NOT haste).

I'm using askmrrobot to decide which gear, reforge, gems etc is best for me and it says that Essence is better then Relic. Why do you suggest that I use Relic instead?

I also tested to use wowreforge, but I just dont understand how you compare diffrent items.

---------- Post added 2013-01-01 at 03:13 PM ----------

I also checked out the Arcane guide here on MMO-champ and like you said jtmzac, they claim that 2/2 relic is better then 2/2 essence.

Why do askmrrobot say the opposite then?

Mr Robot doesn't factor in 6-stack camping (that I'm aware of)

Relic is better than NORMAL EoT because they have SIMILAR (not the same, I'm aware) levels of static Intellect, but Relic procs Intellect, EoT procs Haste. In Mastery build Intellect is far more important than in Haste Build (as you gain more damage per mana % than you would in Haste build); and while the Haste proc from EoT is nice, Relic's Intellect proc is better than the normal version.